approximation of the dorsum of the foot to the front of the leg, while in extension the heel is drawn up and the toes pointed downward. The range of movement varies in different individuals from about 50° to 90°. The transverse axis about which movement takes place is slightly oblique. The malleoli tightly embrace the talus in all positions of the joint, so that any slight degree of side-to-side movement which may exist is simply due to stretching of the ligaments of the talofibular syndesmosis, and slight bending of the body of the fibula. The superior articular surface of the talus is broader in front than behind. In dorsiflexion, herefore, greater space is required between the two malleoli. This is obtained by a slight outward rotatory movement of the lower end of the fibula and a stretching of the ligaments of the syndesmosis; this lateral movement is facilitated by a slight gliding at the tibiofibular articulation, and possibly also by the bending of the body of the fibula. Of the ligaments, the deltoid is of very great powerso much so, that it usually resists a force which fractures the process of bone to which it is attached. Its middle portion, together with the calcaneofibular ligament, binds the bones of the leg firmly to the foot, and resists displacement in every direction. Its anterior and posterior fibers limit extension and flexion of the foot respectively, and the anterior fibers also limit abduction. The posterior talofibular ligament assists the calcaneofibular in resisting the displacement of the foot backward, and deepens the cavity for the reception of the talus. The anterior talofibular is a security against the displacement of the foot forward, and limits extension of the joint.

The movements of inversion and eversion of the foot, together with the minute changes in form by which it is applied to the ground or takes hold of an object in climbing, etc., are mainly effected in the tarsal joints; the joint which enjoys the greatest amount of motion being that between the talus and calcaneus behind and the navicular and cuboid in front. This is often called the transverse tarsal joint, and it can, with the subordinate joints of the tarsus, replace the ankle-joint in a great measure when the latter has become ankylosed.

Extension of the foot upon the tibia and fibula is produced by the Gastrocnemius, Soleus, Plantaris, Tibialis posterior, Peronæi longus and brevis, Flexor digitorum longus, and Flexor hallucis longus; dorsiflexion, by the Tibialis anterior, Peronæus tertius, Extensor digitorum longus, and Extensor hallucis proprius. 1

7e. Intertarsal Articulations

(Articulationes Intertarseæ; Articulations of the Tarsus)

Talocalcaneal Articulation (articulatio talocalcanea; articulation of the calcaneus and astragalus; calcaneo-astragaloid articulation).The articulations between the calcaneus and talus are two in numberanterior and posterior. Of these, the anterior forms part of the talocalcaneonavicular joint, and will be described with that articulation. The posterior or talocalcaneal articulation is formed between the posterior calcaneal facet on the inferior surface of the talus, and the posterior facet on the superior surface of the calcaneus. It is an arthrodial joint, and the two bones are connected by an articular capsule and by anterior, posterior, lateral, medial, and interosseous talocalcaneal ligaments.

The Articular Capsule (capsula articularis).The articular capsule envelops the joint, and consists for the most part of the short fibers, which are split up into distinct slips; between these there is only a weak fibrous investment.

The Anterior Talocalcaneal Ligament (ligamentum talocalcaneum anterius; anterior calcaneo-astragaloid ligament) (Figs. 356, 359).The anterior talocalcaneal ligament extends from the front and lateral surface of the neck of the talus to the superior surface of the calcaneus. It forms the posterior boundary of the talocalcaneonavicular joint, and is sometimes described as the anterior interosseous ligament.

The Posterior Talocalcaneal Ligament (ligamentum talocalcaneum posterius; posterior calcaneo-astragaloid ligament) (Fig. 354).The posterior talocalcaneal ligament connects the lateral tubercle of the talus with the upper and medial part of the calcaneus; it is a short band, and its fibers radiate from their narrow attachment to the talus.

Note 1. The student must bear in mind that the Extensor digitorum longus and Extensor hallucis proprius are extensors of the toes, but flexors of the ankle; and that the Flexor digitorum longus and Flexor hallucis longus are flexors of the toes, but extensors of the ankle. [back]